How Much of Hulu's The Great Is Real History, and How Much Is Totally Fictional?

Most of the characters at court are fictional and created just for The Great, although they're based on types of people who would have been at Peter and Catherine's court. Catherine's maidservant and best friend, Marial, is a complete invention, as are the courtiers who surround them. The court was filled with Russian nobility, all striving to be favored by the rulers, and it's likely that there was every bit as much intrigue as The Great depicts.